Method and device for regulating the boost pressure of an internal combustion engine

ABSTRACT

The turbine ( 4 ) of the exhaust gas turbocharger, which is located in the exhaust gas channel ( 3 ) of the internal combustion engine ( 1 ), has a variable geometry. The regulation of the boost pressure (pld) is performed via an adjustment of the turbine geometry. A very rapid response of the boost pressure regulation to a variable load, with an overshoot of the specified value, which would damage the turbocharger, being avoided, is achieved by determining a manipulated variable (vtg) for the turbine geometry as a function of the exhaust gas back pressure (pag) prevailing in the exhaust gas channel ( 3 ) upstream from the turbine.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and a device forregulating the boost pressure of an internal combustion engine having anexhaust gas turbocharger whose turbine, which is located in the exhaustgas channel of the internal combustion engine, has an adjustablegeometry, with the regulation of the boost pressure occurring via anadjustment of the turbine geometry.

BACKGROUND INFORMATION

[0002] As it is provided in, for example, German Published PatentApplication No. 41 07 693 or European Published Patent Application No.04 54 943, boost pressure regulation is typically performed by acontroller producing a manipulated variable as a function of thedeviation between a specified boost pressure and an actual boostpressure. This manipulated variable is used either for controlling avalve in a bypass which bypasses the turbine of the turbocharger in theexhaust gas channel (see German Published Patent Application No. 41 07693) or for controlling the adjustable turbine guide vanes of a turbinehaving variable geometry (see European Published Patent Application No.04 54 943).

[0003] Increasingly higher requirements are placed on engines in regardto exhaust gas and consumption characteristics. An exhaust gasturbocharger having variable turbine geometry allows an adjustment tothe current engine operating point through adjustment of the turbineguide vanes. With this technique, a delayed response of the exhaust gasturbocharger (turbo lag) can be reduced and the efficiency of the enginecan be improved at the same time. Overshoots of the boost pressure,which mechanically stress the turbocharger very strongly, often occurduring acceleration operations. In addition, excessive closing of thevariable turbine geometry in the acceleration phase can result in anunwanted high exhaust gas back pressure, which negatively influences thedynamic response and efficiency of the engine.

SUMMARY OF THE INVENTION

[0004] The present invention therefore has as its object the provisionof a method and a device for boost pressure regulation of the type citedinitially which ensure that the boost pressure follows the course of thedesired boost pressure specified value as rapidly as possible in thecase of an alternating load, with an overshoot of the boost pressurespecified value being avoided to protect the exhaust gas turbochargerfrom unnecessarily high loads.

[0005] The object cited is achieved in that a manipulated variable forthe turbine geometry is determined as a function of the exhaust gas backpressure prevailing in the exhaust gas channel upstream from theturbine. The exhaust gas back pressure responds significantly fasterthan the boost pressure to changed behavior of the controlledsystem—e.g., speed change, alternating load, change in exhaust gasrecirculation—or to malfunctions, e.g., in the servo-system. Therefore,if the exhaust gas back pressure is used according to the presentinvention to derive a manipulated variable, a very rapid response of theboost pressure regulation to a change in the preset specified boostpressure is achieved.

[0006] An advantageous refinement of the method according to the presentinvention and the device according to the present invention is that aspecified exhaust gas back pressure is determined by a first controllerfrom the deviation between a specified boost pressure and an actualboost pressure, and the manipulated variable for the turbine geometry isderived by a second controller from the deviation between the specifiedexhaust gas back pressure and a measured or estimated actual exhaust gasback pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 shows a schematic view of an internal combustion enginehaving an exhaust gas turbocharger.

[0008]FIG. 2 shows a flowchart for the regulation of the boost pressure.

DETAILED DESCRIPTION

[0009]FIG. 1 shows an internal combustion engine I having an intakechannel 2 and an exhaust gas channel 3. Turbine 4 is located in exhaustgas channel 3 and compressor 5 of an exhaust gas turbocharger is locatedin intake channel 2. Furthermore, the internal combustion engine can beequipped with an exhaust gas recirculation channel 6 which connectsexhaust gas channel 3 with intake manifold 2. A controllable valve 7 islocated in exhaust gas recirculation channel 6. A pressure sensor 8 formeasuring boost pressure pld and an air mass flow sensor 9 for measuringair mass flow intake lm are located in intake manifold 2. In addition,there is a butterfly valve 10 in the intake manifold. A sensor 11detects the speed nmot of the internal combustion engine, and a pressuresensor 12 in exhaust gas channel 3 measures exhaust gas back pressurepag upstream from turbine 4. An actuator 13 is present which acts on theturbine geometry, i.e., performs an adjustment of the turbine guidevanes. This actuator 13 receives a manipulated variable vtg from acontroller 14. Controller 14 uses motor speed nmot, butterfly valveposition dk, airflow intake lm, boost pressure pld, and exhaust gas backpressure pag as the input variables to derive manipulated variable vtgfor the turbine geometry and a manipulated variable arf for the exhaustgas recirculation valve.

[0010] The procedure that controller 14 uses for deriving manipulatedvariable vtg for the turbine geometry from the input variables citedwill be described in more detail with reference to the flowchart in FIG.2. A processor PZ determines a specified boost pressure plds from motorspeed nmot, butterfly valve setting dk, which reflects the intent of thedriver, and possibly other operating quantities of the engine notmentioned here. The derivation of specified boost pressure plds will notbe discussed in more detail here, because it is part of the related art.Deviation Δpld between specified boost pressure plds and an actual boostpressure pld is determined in a first node V1. Deviation value Δpld forthe boost pressure is supplied to a first controller R1 (e.g., PI or PIDcontroller). The output quantity of first controller R1 corresponds to aspecified value pags of the exhaust gas back pressure in exhaust gaschannel 3. Deviation Δpag between specified exhaust gas back pressurepags and actual exhaust gas back pressure pag is established in a secondnode V2. Deviation value Δpag for the exhaust gas back pressure issupplied to a second controller R2, which finally produces manipulatedvariable vtg for the variable turbine geometry.

[0011] Actual boost pressure pld can either be measured by way ofpressure sensor 8 in intake manifold 2, or an estimate for the actualboost pressure can be derived by processor PZ from various operatingquantities of the internal combustion engine. The dot-dash line in FIG.2 indicates that actual boost pressure pld is an estimate determined byprocessor PZ. Actual exhaust gas back pressure pag can be a measuredvalue of pressure sensor 12 in exhaust gas channel 3. However, actualexhaust gas back pressure pag can also be an estimate derived byprocessor PZ from operating quantities of the internal combustionengine. The dot-dash line leading from processor PZ to second node V2indicates that actual exhaust gas back pressure pag is an estimatecalculated by processor PZ. The calculation of the estimates for actualboost pressure pld and actual exhaust gas back pressure pag will not bediscussed in more detail here, because methods known from the relatedart can be used in this case.

[0012] Exhaust gas back pressure pag in exhaust gas channel 3 upstreamfrom turbine 4, and thus also the energy injected into turbine 4,increase through closing of the turbine geometry. For this reason, theturbocharger speed and, at the same time, boost pressure pld in intakemanifold 2 increase. If there is exhaust recirculation, as shown in FIG.1, exhaust gas can reach the intake manifold via exhaust gasrecirculation channel 6 by opening valve 7, if exhaust gas back pressurepag is greater than boost pressure pld. If exhaust gas recirculationvalve 7 is opened, exhaust gas back pressure pag, and therefore alsoboost pressure pld in intake manifold 2, drop.

[0013] The present invention is based on the observation that exhaustgas back pressure pag responds significantly faster to an adjustment ofthe turbine geometry than boost pressure pld. Boost pressure pldresponds only with a delay equal to the time constant of the exhaust gasturbocharger. Therefore, the dynamic of a controller for the boostpressure is essentially limited by the moment of inertia of the exhaustgas turbocharger. The time constant occurring in this case is, however,significantly larger than the time constant of several disturbanceswhich act on the system through the time-variant behavior of thecontrolled system, through opening and closing of exhaust gasrecirculation valve 7, or through errors in the guide vane system ofturbine 4. Disturbances of the guide vane system of the turbine, changesin the valve lift of exhaust gas recirculation valve 7, or changes inthe operating point of the internal combustion engine affect exhaust gasback pressure pag very directly and can therefore be compensated forvery rapidly in the lower-level control loop having controller R2. Theupper-level control loop having controller R1 is designed as slower thanthe lower-level control loop having controller R2. However, since boostpressure pld is more sluggish than exhaust gas back pressure pag anyway,this condition is fulfilled automatically.

What is claimed is:
 1. A method for regulating the boost pressure of aninternal combustion engine having an exhaust gas turbocharger whoseturbine (4), which is located in the exhaust gas channel (3) of theinternal combustion engine (1), has an adjustable geometry, with theregulation of the boost pressure occurring via an adjustment of theturbine geometry, wherein a manipulated variable (vtg) for the turbinegeometry is determined as a function of the exhaust gas back pressure(pag) prevailing in the exhaust gas channel (3) upstream from theturbine (4).
 2. The method according to claim 1, wherein a specifiedexhaust gas back pressure (pags) is established by a first controller(R1) from the deviation (Δpld) between a specified boost pressure (plds)and an actual boost pressure (pld), and the manipulated variable (vtg)for the turbine geometry is derived by a second controller (R2) from thedeviation (Δpag) between the specified exhaust gas back pressure (pags)and a measured or estimated actual exhaust gas back pressure (pag).
 3. Adevice for regulating the boost pressure of an internal combustionengine having an exhaust gas turbocharger whose turbine (4), which islocated in the exhaust gas channel (3) of the internal combustion engine(1), has an adjustable geometry, with the regulation of the boostpressure occurring via an adjustment of the turbine geometry, wherein acontroller (R2) produces a manipulated variable (vtg) for the turbinegeometry as a function of the exhaust gas back pressure (pag) prevailingin the exhaust gas channel (3) upstream from the turbine (4).
 4. Thedevice according to claim 3, wherein a first controller (R1) determinesa specified exhaust gas back pressure (pags) from the deviation (Δpld)between a specified boost pressure (plds) and an actual boost pressure(pld) and a second controller (R2) derives the manipulated variable(vtg) for the turbine geometry from the deviation (Δpag) between thespecified exhaust gas back pressure (pags) and a measured or estimatedactual exhaust gas back pressure (pag).